In this article we will discuss about the culture of air-breathing fishes.
Air-breathing fishes are characterised by the possession of an accessory respiratory organ. This organ enables the fishes to remain for hours out of water or for indefinite period in oxygen poor waters and even in moist mud. They are extremely hardy with respect to all environmental parameters and are suited to shallow foul waters, weedy waters of ponds and swamps.
These fishes have commercial value as they are marketed in living condition and hence they are also referred to as ‘live fishes’ or ‘jeol fishes’. The air-breathing fishes are highly priced and are well- known for their high protein, high iron, low fat- content and easy digestibility and are thus recommended by physicians as diet during convalescence.
The culture of these fishes involves low risk and simple management. In spite of their high economic value, their cultivation has not been widely practised. Generally, due to their carnivorous feeding behaviour they are eliminated from polyculture ponds.
However, if the culture of these air breathing carnivorous fishes is undertaken in shallow water pond (which is unsuitable for carp culture due to the low height of standing water), it would prove a more profitable venture.
Moreover, these fishes adapt excellently to supplementary feeding with dried marine trash fish, oil cake and rice bran. Magur (Clarius batrachus) and Singhi (Heteropneustes fossilis) are known to be feeding on gastropods, microcrustaceans, tubificid worms, insects and larvae.
Koi (Anabas testudineus) is generally micro-plankton feeder in younger stages and takes to insectivorous feeding habit in later stages. Koi also responds favourably to feed oriented culture with oil cake and rice bran.
Air-breathing fishes, at present, form the bulk and main stay of tank fisheries in India. The states of Andhra Pradesh, Assam, Bihar, Karnataka. Madhya Pradesh, Meghalaya, Maharashtra, Orissa, Tamil Nadu, Uttar Pradesh and West Bengal, support the most significant natural fishery of air-breathing fishes.
Advantages of Culturing Air-Breathing Fishes:
Air-breathing carnivorous fishes are cultivated due to the following reasons:
(1) They have high protein, high iron and low fat content and are thus more nutritious and of high medicinal value.
(2) They have a high market demand and fetches a high price than other edible fishes.
(3) As air-breathing fishes have accessory respiratory organs, their culture can be undertaken in rejected foul water of shallow ponds, swamps, weedy waters and other kinds of oxygen depleted water bodies.
(4) They are hardy fishes and can adjust to any environmental conditions.
(5) They require little rearing.
(6) Their culture involves less risk.
(7) Their culture management is simple without much complications.
(8) They grow faster (particularly the exotic magur) when sufficiently fed.
(9) They are voracious carnivores and devours any type of flesh.
(10) In case of cage or pen culture, the yield is more and hence the income increases many- fold.
(11) They are highly recuperative.
(12) Their culture can lead to reclamation of previously unused derelicts.
Cultivable Species of Air-Breathing Fishes in India:
The cultivable species (Fig. 6.42) among cat- fishes (presence of small to very long barbels like the whiskers of cats) are Indian magur (Clarias batrachus) and Snighi (Heteropneustes fossilis).
Among the murrels (snake-headed fishes) are the giant murrel (Channa marulius), stripped murrel (C. striatus) and spotted murrel (C. punctatus) are the cultured species. While in the case of climbing perch the species favourable for culture is Koi (Anabas testudineus).
Among the two exotic magur cultured of commercial importance, the African catfish or Nile catfish C. lazera/C.gariepinus (Fig. 6.41) (often wrongly called as hybrid magur by common man) has received greater attention because of its voracious (carnivore) eating and faster growth rate. The other exotic catfish C. macrocephalus, with slower growing rate, has a higher consumer preference.
Cultural Practices of Air-Breathing Fishes:
The culture of air-breathing fishes is done by the following ways:
(a) Pond culture
(b) Swamp culture
(c) Cage and pen culture, and
(d) High-density culture.
A. Cultivable areas:
Culture of air- breathing fishes is equally adaptable in carp culture ponds as well as in waters unsuitable for conventional culturable species of carps. They can be grown under poor environmental conditions. Culture is generally done in shallow water area of 0.1 ha with a depth of 2-3 feet (or 50-75 cm).
Shallow water depth has an advantage as the fish has to spend less energy in travelling to surface for intake of atmospheric oxygen. Cultivation of these fishes is also done in nursery ponds during the period these ponds remain fallow (after harvesting of carp fry).
India has an estimated 0.6 million hectare of water that has remained unutilised for fish production. This area comprises marshes and swamps whose difficult ecology has made it derelict. West Bengal, Kerala, Bihar and Assam has such extensive areas under swamp conditions.
These water bodies are potentially rich but are difficult for fish culture. Reclamation has been made possible with the introduction of cage-culture method of raising air-breathing fishes.
The two main obstacles of swamp culture that can be overcome with cage culture practices are:
(1) The risk of raised fish being lost can be eliminated through cage-culture.
(2) The deoxygenated conditions of swamps which leads to mass kill, can be eliminated through culture of air-breathing fishes.
Preliminary experiments has revealed a production of over 1.2 tons/ha/7 months culture with singhi, magur and koi. Added to this would be the income through culture of makhana’ cash crop from the same swamp.
(c) Cage Culture:
Cage culture of air-breathing fishes is generally undertaken in swamps, running water systems like streams, raceways and channels and unmanageable water bodies like reservoirs. The cages used for culture may be floating nylon cages of 1 m x 1 m x 1 m, supported with wooden reapers, or bamboo cages of 2 m x 1 m with a depth of 0.8 m.
Constant flow of water helps to bring food and wash away the waste products. Cage culture of air-breathing fishes particularly in the case of climbing perch (koi) has eliminated the risk of raised fishes being lost, thereby increasing the yield. Fry of these fishes are sometimes grown in floating baskets. The feed given in cages are the same as given in ponds.
Koi stocked at the rate of 50-100/cage and fed (at the rate of 10% of body weight) on rice bran, mustard oil cake and silkworm pupae can give a production of 1.3 kg/m3/3 months of culture. Magur with a high stocking rate of 200/cage and fed (10% of body weight) with dried trash fish, oil cake and rice bran can yield 9.9-12 kg/m3/1 year.
As air-breathing fishes fetch a high price in the market, it may permit even enhanced expenditure to improve their culture system. This would lead to higher yield in the long run.
(d) High Density Culture:
High density tank culture of air-breathing fishes in recirculating water system has been tried on an experimental scale. Although this has been found to be profitable yet it has not been adopted for commercial production.
B. Pond Management:
Pond culture of air-breathing fishes is essentially a short duration one. Pond management is very simple. Unlike carp culture, the ponds for air-breathing fish culture need not be fertilised by chemical or organic fertiliser. The only input materials are the fingerlings (6-10 gm each) and feed. In case of very heavy stocking rate and multiple cropping, replenishment of water becomes essential to obtain high yield.
However, for effective management, the pond should not be more than 0.1 to 0.2 ha in size. In case, the pond (even perennial ponds) is found to be infested with predators or predatory fishes it is essential to kill them with the application of mahua oil cake at the rate of 2500 kg/ha.
After 15 days of treatment with mahua oil cake, the pond bottom is raked by dragging a few bricks tied to a rope. This liberates unwanted toxic gases, etc. If the bottom silt is very heavy, then lime is added at the rate of 300 kg/ha which will not only reduce the toxicity of gases but will also enhance the fertility of the pond.
For culturing air-breathing fishes, the inner sides of the pond should be either made firm with heavy log or wood, or fenced with bamboo cane or wire screens to a height of about 50 cm. This would prevent the air- breathers from escaping the pond water through climbing or burrowing.
C. Seed Collection and Transport:
Seeds of magur, singhi and murrels can be collected both by induced breeding as well as from the wild.
Seeds collected from nature are dependable, as the fry of these fishes can be identified as given below:
(1) Fry of giant murrel (Channa marulius) is identified by its dark grey body and a lateral orange yellow band running from eye to the caudal fin.
(2) The stripped murrel (C. striatus) fry can be recognised by their vermillion red body with reddish golden band and a dark black band running from the eye to the caudal fin.
(3) Fry of the spotted murrel (C. punctatus) can be identified by their dark brown body with a golden yellow lateral band and a mid-dorsal yellow line on the back.
(4) Fingerlings of magur (Clarias batrachus) can be recognised by their slate colour and long dorsal fin.
(5) Singhi (Heteropneustes fossilis) fingerlings can be identified by their pinkish colour and shorter dorsal fin.
(6) Koi (Anabas testudineus) fingerlings are known by the dark spot on the caudal peduncle and greenish hue of the dorsal body surface.
(a) Seed Collection of Murrel:
Murrels attain maturity in about two years. As they are known to breed throughout the year, the fry (2-4 cm) can be collected round the year from rain-fed ditches and shallow water bodies among abundant weeds. Their peak spawning occurs, however, during April to June with the onset of monsoon.
As the hatchlings move in schools, their collection in large numbers is always possible. It may be noted that when the fry reaches the fingerling stages they do not move in schools. Collection of murrel seed is generally made during monsoon.
Murrel seed can also be produced by induced breeding, but the difficulty lies in maintaining the spawn and growing them to fry stage. As the spawns after emergence from eggs do not feed on anything for about two days, their survival rate will generally be poor. For this, the hatchlings are required to be reared in suitable cemented ponds or plastic pools and have to be trained to take supplementary feed.
(b) Seed Collection of Catfishes:
The matured male of magur possesses a pointed anal papilla, while that in female is oval in shape. Though cat- fishes breed throughout the year, the peak season for the collection of seed is pre-winter period when paddy is harvested and the low lying fields get exposed. Spawning generally takes place in fairly deep waters. The female makes a hole of 20 cm diameter and 25 cm deep on the bottom.
The fertilised eggs measuring 1-1.5 mm (diameter) are yellowish-brown in colour and adhere to grasses. The males guard the eggs till it hatches within 20 hours at a temperature of about 25-30°C. About 2000 to 15,000 fries per hole can be collected from natural areas with the help of a small fine-meshed hand-net. They are then reared in nurseries till they reach a length of 5 cm.
In case of pond breeding, compartments or enclosures of 1 m x 1 m are made of wire screen in the pond having a water depth of about 25 cm. At the centre of each compartment a hole of 30 cm diameter is dug up to a depth of 25 cm.
The holes are provided with some aquatic plants. The matured male and female fishes suitable for breeding are put into each compartment and they spawn within a period of 10 days. A maximum of 5,000 fry are collected from each compartment.
Seeds of catfishes can also be collected through induced breeding. The effective dosage of pituitary extract for different sized fishes is as follows:
(1) For catfishes weighing less than 100 gm is 10 mg extract.
(2) For catfishes weighing 100-150 gm is 25 mg extract.
(3) For catfishes weighing 150-200 gm is 35 mg extract.
Within 15 hours spawning takes place and the eggs thus produced is placed in shallow troughs or hatching jars. The water of the jars is changed twice a day preferably during the morning hours. After about 20 hours, the eggs hatch and the yolk sac attached to the hatchling remains for five days till they are completely absorbed.
(c) Transport of Seeds:
Fry of air-breathing fishes are generally transported without oxygen packing. The fry transported in carrier (usually polythene drum or iron drum) have enough of open space for their habitual surfacing to breath atmospheric air.
If the period of transportation is less than five hours and the fingerlings are kept in open and watering tin carriers or in mud pots then a small quantity of aquatic weeds (Hydrilla, Vallisneria, Ceratophyllum, etc.) are placed on it. This would prevent the fingerlings from jumping out of the pot.
D. Nursery Management:
The fry rearing phase in murrels is a bit complex due to its cannibalistic habit. This can be reduced with sufficient supplementary feeding. High survival rate can be achieved through supplementary feeding and addition of micronutrients, yeast and vitamin B.
Nursery ponds of about 10-15 m2, having a water column of 50 cm are stocked with 0.2 to 1.5 million fry per hectare. Prior to stocking, manuring is done with cow dung at the rate of 500 kg per hectare. To keep the nurseries free from insects, soap emulsion has to be applied.
Advanced fry and fingerlings of catfishes collected from natural source do not require nursery management. Murrels, on the other hand, has to be trained to accept artificial feed prior to stocking in nursery ponds.
E. Stocking of Fingerlings:
Stocking of air breathing fishes is done at high density, and uniform sized fingerlings should be chosen. In case of monoculture of either magur or singhi, the stocking rate recommended in ponds is 40,000-60,000 fingerlings per hectare of water area.
In case of poly-culture with carps, magur may be cultured in place of common carp. Fingerlings of this catfish may be stocked at the rate of 20,000-30,000 fingerlings per hectare along with the recommended stocking density of carps.
Giant murrels, stripped murrels and spotted murrels may be stocked for monoculture at the rate of 15,000, 20,000 and 25,000 fingerlings per hectare, respectively. In the case of mixed culture, the latter two species may be stocked at the rate of 20,000 fingerlings per hectare at a ratio of 1: 1. In case of murrel culture also, uniform sized fingerlings raised in nurseries are selected that are trained to accept artificial feed.
The selected fishes before stocking should be given a dip in 200 ppm (mg/1) formalin solution for 40 seconds or treated with 2% potassium permanganate solution for about five minutes. During periodic check on growth, the wounded fish, if any, may be treated with 0.3% acriflavin for five minutes.
Successful culture of air-breathing fishes depends upon stocking of the right size of fingerlings (6-10 gm), along with regular feeding and health checking of the fish stock. In case of mixed farming of murrels or catfishes with carps, the seeds of air-breathing fishes should be stocked only when the carps have reached a minimum size of 300 gm.
This would safeguard the carps from being preyed upon by the air- breathing fishes. This practice of mixed culture not only provides an additional income through the yield of air-breathing fishes, but it also enhances the growth of carps. Such increase in growth of carps is possible as the air-breathing fishes would prey upon the trash fishes which may compete with culturable carps for food and space.
F. Feeding and Feed Schedule:
To maintain an abundant food supply for the growing fingerlings of the air-breathing fishes, it is essential that the stocking pond be rich in animal food source such as tadpoles and trash fishes. In case these food sources are found to be inadequate, tilapia may also be grown, so that the young of tilapia (which is a fast breeder) may serve as a regular and staple food source for the fingerlings of cat fishes and murrels.
In case of maritime states (West Bengal, Orissa, Kerala, Andhra Pradesh, etc.), abundant availability of dried marine trash fish would make the culture of air-breathing fishes more economical. However, in ponds where the above facilities are not available, then one has to resort to supplementary feeding.
Artificial feeding for singhi and magur is undertaken using fish offal or slaughter house waste or dried silkworm pupae mixed with rice bran and oil cake in the ratio of 1:1:1.
A mixture of rice bran, mustard oil cake and trash fish meal in the ratio 2:1:1; rice bran and poultry feed in 3:1; biogas slurry and rice bran in 1:2 or poultry dropping and rice bran in 1:2 ratio may also be given daily at the rate of 5-8 per cent of body weight of the fish fingerlings stocked.
Air-breathing catfishes during their six-month semi-intensive culture in stagnant ponds may be fed by the way given in Table 6.11.
On the other hand, trained fingerlings of murrel may be provided with cheaply available dried marine trash fish soaked in water, in the feeding schedule given in Table 6.12, during their eight-month semi- intensive culture.
Feeding may be done either by broadcasting the feed in small amounts on all sides of the embankment, till the fish stops feeding or may be served in feed baskets, lowered near the banks. Feed baskets may also be given in addition to broadcasting of feed, so as to ensure feed availability to all the fishes in the pond.
It is interesting to note that catfishes and murrels come in shoals when the feed baskets are lowered in the pond water. It has been observed that better feed utilisation takes place in the case of catfishes, when they are fed during dark hours.
G. Culture Duration and Production:
Satisfactory response to external feeding results in good growth. Magur and singhi are expected to attain a weight of about 120 gm and 50 gm, respectively in 6 months of culture, whereas giant murrel, stripped murrel and spotted murrel grow to a size of about 400 gm, 275 gm and 160 gm, respectively in 7-8 months of culture period.
Air-breathing fishes when cultured under high input technology (semi-intensive) of both mono- and mixed- culture practices, the production potential of the following type can be obtained:
(1) A production of about 5 tonnes/hactare/6 months of magur can be obtained with supplementary feed made of dried trash fish and rice bran.
(2) An yield of 5.1 tonnes/hactare/14 months of singhi culture can be obtained with supplementary feed made of rice bran and trash fish.
(3) Murrel’s production of 4 tonnes/hectare/10.6 months culture can be obtained on being fed with forage fish.
(4) Mixed culture of magur and singhi when fed with rice bran and trash fish a production of 5 tonnes/ hectare/year culture can be obtained.
(5) Mixed culture of murrel and koi when fed with rice bran, mustard oil cake and trash fish may result in a production of 5.9 tonnes/hectare/6 months.
(6) Mixed culture of the three murrel species can yield about 4 tonnes/hectare/year when fed with soaked dried marine trash fish and fresh silkworm pupae.
(7) In intensive culture, the production of magur and singhi can be increased to about 7.8 tonnes and 7 tonnes respectively/hectare/5 months culture when fed with fish meal and rice bran.
In carp polyculture system magur is cultured in place of common carp. Magur, singhi and koi can also be cultured along with makhana (Euryale ferox), a highly priced aquatic crop, in the same shallow pond.
Generally harvesting of air-breathers is done in summer season from production ponds when the depth of water is less. The pond water is drained out and the fishes are harvested with the help of a hand-net or scoop-net.